The limits on the 360 were a mix of file system limits and also the fact that they made money selling you a bigger HDD drive. The past doesn't however indicate what will happen in the future so if you look at where MS is taking the XB1, as they've said it's Windows, and it can run universal Windows apps. The odds of it using the same file system as Windows devices, which is NTFS now and not FAT32 is high. Actually I wouldn't be surprised if when they do introduce external storage support on the XB1 it'll be a case of the drive either being used to read off of, for music/videos etc but when/if you want it to store games on it then it'll have to be encrypted (for piracy protection and all that), probably a case of NTFS EFS + Bitlocker so that you can't install games to it and then read them off to any old PC etc.

The delay in getting the feature is, and I'm guessing here, because they want to make it secure enough yet also portable, though that part is something I hope for. It'd be great if you could take it with you, connect it to any XB1 and just access the content after you login with your account. It's possible really, they can tweak bitlocker and so on to work that way.